In reflection seismology, azimuthal amplitude gradient represents the change in reflected seismic amplitude with respect to source-receiver azimuth. It is often desirable to use the azimuthal amplitude gradient, derived from seismic data, to determine orientation and magnitude of reservoir fractures and of geologic stress fields. Conventionally, azimuthal amplitude gradient is typically estimated at each point separately in a seismic survey. However, this point-wise estimation approach can be limited by various factors such as noise, data misalignments at different azimuths, and ambiguity between gradient polarity and symmetry azimuth.
One method of determining or estimating azimuthal amplitude gradient is known as amplitude variations with azimuth (AVAZ). AVAZ analysis takes advantage of the fact that rocks often exhibit different properties along paths of maximum and minimum stress and/or along paths parallel and perpendicular to fractures. A fundamental ambiguity in AVAZ analysis has been recognized for some time and can be seen in FIG. 2 (discussed later).